Today's consumer electronics market frequently demands complex functions requiring very intricate circuitry. Scaling to smaller and smaller fundamental building blocks, e.g. transistors, has enabled the incorporation of even more intricate circuitry on a single die with each progressive generation. Semiconductor packages are used for protecting an integrated circuit (IC) chip or die, and also to provide the die with an electrical interface to external circuitry. With the increasing demand for smaller electronic devices, semiconductor packages are designed to be even more compact and must support larger circuit density. Furthermore, the demand for higher performance devices results in a need for an improved semiconductor package that enables a thin packaging profile and low overall warpage compatible with subsequent assembly processing.
C4 solder ball connections have been used for many years to provide flip chip interconnections between semiconductor devices and substrates. A flip chip or Controlled Collapse Chip Connection (C4) is a type of mounting used for semiconductor devices, such as integrated circuit (IC) chips, MEMS or components, which utilizes solder bumps instead of wire bonds. The solder bumps are deposited on the C4 pads, located on the top side of the substrate package. In order to mount the semiconductor device to the substrate, it is flipped over—the active side facing down on the mounting area. The solder bumps are used to connect the semiconductor device directly to the substrate. However, this approach may be limited by the size of the mounting area and may not readily accommodate stacked die.
Accordingly, hemispherical C4 solder bumps are formed above an insulation layer and above the exposed surfaces of connector pads (also known as bump pads), each of which is exposed through a via hole in the insulation layer or layers. Subsequently, the solder bumps are heated above their melting point until they reflow and form a connection with the Cu stud bumps of the die. The actual C4 solder bumps may be fabricated using a number of different processing techniques, including evaporation, screen printing, and electroplating. Fabrication by electroplating requires a series of basic operations which typically include the deposition of a metallic seed layer, the application of an imaged photo-resist (in the pattern of C4 solder bumps), the electro-deposition of solder, the stripping of the photo-resist, and the sub-etching of the metallic seed layer to isolate the C4 bumps.
On the other hand, conventional wire-bonding approaches may limit the number of semiconductor die that can reasonably be included in a single semiconductor package. Furthermore, general structural issues may arise when attempting to package a large number of semiconductor die in a semiconductor package. Accordingly, additional improvements are needed in the evolution of semiconductor packages.